The present invention relates to a novel method of applying borosilicate containing coatings on electronic substrates. The novelty herein resides in the fact that borosilazane polymers are used as borosilicate precursors.
Various methods for the application of ceramic coatings on electronic devices are known in the art. For instance, it is known to use gaseous precursors in a variety of vapor deposition processes to produce coatings of silica, silicon nitride, silicon oxynitride, silicon carbide and the like . These coatings are taught to be useful as protective and dielectric layers.
Similarly, the use of polymeric precursors for depositing ceramic coatings on electronic devices is also known in the art. For instance, Haluska et al. in U.S. Pat. Nos. 4,749,631 and 4,756,977 and the Accuglass.TM. product literature disclose silica coatings produced by applying solutions of silica precursors to the devices and then heating the coated devices to convert the precursors to silica. These references, however, do not disclose the use of borosilazanes.
The use of polysilazanes for applying silicon, carbon and nitrogen containing ceramic coatings on electronic devices is also known in the art. For example, Haluska et al. in U.S. Pat. Nos. 4,756,977 and 4,826,733 teach forming ceramic coatings by applying coatings of silicon and nitrogen containing polymers such as polysilazanes on such devices and then heating the coated devices in an inert atmosphere. When the coatings are heated, as taught, in an inert atmosphere the nitrogen is maintained in the coating and, thus, silicon nitride or silicon carbonitride is formed.
U.S. Pat. No. 4,973,526 also teaches a method of forming coatings containing silicon, oxygen and boron. The method taught therein comprises mixing hydrogen silsesquioxane resin with a boron oxide precursor, coating an electronic device with the mixture and heating the coated device to ceramify the coating. It is clear, therefore, that the reference does not describe the use of borosilazanes.
Finally, it is known that references such as U.S. Pat. Nos. 4,482,689 and 4,910,173 and European Patent Nos. 364,323 and 424,082 teach the use of borosilazanes to form coatings. These references, however, do not teach the use of such materials on electronics and the coatings derived therefrom are not borosilicates.
The present inventors have now discovered that borosilicate containing coatings derived from borosilazane polymers can be applied on electronic substrates. Since the resultant coatings are thick, planar and defect free, they can be used as protective and dielectric layers.